Mining semantics contract drift: interval empty blocks and explicit intervalSeconds handling

[roninjin10]

Summary

Trusted mining behavior diverges from the contract in three places:

1. Interval mining does not produce empty blocks when no tx is pending.
2. Explicit mine calls ignore the second intervalSeconds argument.
3. Interval-mining setter treats input as milliseconds and rounds, while contract defines seconds.

Why this matters

Mining cadence and timestamp progression semantics are part of the public contract and directly affect tests, replay determinism, and tooling behavior.

Normative contract

• docs/specs/json-rpc-contract.md:866-868 interval mode should produce empty blocks when idle.
• docs/specs/json-rpc-contract.md:876-879 explicit mine supports [count, intervalSeconds].
• docs/specs/json-rpc-contract.md:749 zevm_setIntervalMining parameter is seconds.

Evidence

Interval loop exits when pool is empty:

• src/rpc/node_handler.zig:1148-1150

if (self.node_runtime.pool.pendingCount() == 0) {
    return;
}

Explicit mine only parses first arg (count) and ignores second arg:

• src/rpc/node_handler.zig:439-443

const count = parseOptionalFirstU64(params, 1) ...
while (i < count) {
    ...
}

Interval setter converts provided value as milliseconds to seconds:

• src/rpc/node_handler.zig:402-410

const interval_millis = parseOptionalFirstU64(params, 0) ...
const interval_seconds = @max(@as(u64, 1), (interval_millis + 999) / 1000);

Suggested scope

• Remove pending-pool gate in interval loop so empty ticks can seal empty blocks.
• Parse and apply explicit mine second arg (intervalSeconds) for per-call timestamp stepping.
• Align interval setter units with contract seconds semantics.
• Add end-to-end tests for:
  • interval mode empty-block production,
  • multi-block explicit mine with timestamp increments,
  • unit-correct interval configuration.